1. Field of the Invention
The present invention relates to a magnetic head for perpendicular recording and a magnetic disk storage apparatus provided with the head mounted thereon.
2. Description of the Related Art
In general, the magnetic disk storage apparatus is composed so that data may be read or written on a recording medium by using a magnetic head. In order to increase a recording density per a unit area of a magnetic disk, it is necessary to decrease a size of recording bit. In the longitudinal magnetic recording system, however, a smaller recording bit disadvantageously causes a recording written magnetization on a medium to be lost by thermal fluctuation. This disadvantage brings about difficulty in enhancing the recording density. As the effective technique in overcoming this difficulty, the perpendicular recording system may be referred which is composed to record (or write) the magnetization in the perpendicular direction to the medium.
The perpendicular recording system may be roughly divided into one system composed to have a double layered perpendicular medium consisting of a recording layer served as a recording medium and a soft under layer and the other system composed to have a single layered perpendicular medium having no under layer. The system composed to use the double layered perpendicular medium as a recording medium needs the so-called single pole type head provided with a main pole and an auxiliary pole for writing data.
The provision of the soft under layer leads to increasing a writing magnetic field strength obtained by the write head but also leads disadvantageously to giving rise to a failure caused by the under layer itself. For example, magnetization on the under layer is changed according to the recorded bits on the recording layer and the write head field. This change brings about a magnetic field, which may disturb the writing bits written on the recording layer or be observed as noise when reading the magnetizing signal with a read element. Moreover, a certain kind of distribution of the change of magnetization may bring about a large magnetic field from the under layer.
A magnetic head having a plurality of auxiliary poles and coils has been known, an exemplary one of which is described in the following patent publication 1 and non-patent publication 1. The techniques disclosed in these publications are prepared for a stray field and do not make any allowance for the ratio of the magneto-motive force of a coil. Further, if the head is structured to have only one auxiliary pole, the coils are located symmetrically. This structure disables to suppress the noise caused by the change of magnetization of the under layer.
Patent Publication 1 . . . Official Gazette of Japanese Patent Laid-open No. 2001-250204
Non-patent Publication 1 . . . Pages 163 to 168 of IEEE Transactions on Magnetics. Vol. 38, No. 1, 2002